1. Field of the Invention
Heretofore, compositions and processes of the prior art in which nitrogen-sulfur fluids are produced using either ammonium sulfate or a combination of sulfuric acid and ammonia have for the most part been restricted to being solutions of low-grade and low-sulfur content because of the relatively low solubility of ammonium sulfate in various other fertilizer fluids. Other nitrogen-sulfur fluid fertilizers containing ammonium sulfate and produced by the practice of the teachings of the prior art also contain other more soluble fertilizer materials, but these other more soluble materials have the disadvantage that they cause the suspensions to have relatively poor physical and handling properties as well as poor long-term storage characteristics. Fertilizer materials which are highly soluble in water or other fertilizer solutions are considered to be more desirable than materials with low solubility, because higher-grade fluid fertilizers can be produced with the more soluble materials. In producing solution fertilizers, in which no fertilizer solids are to be present, use of more highly soluble fertilizer materials allows for more plant food (higher grade) to be in solution without crystallizing out at a given temperature than when a less soluble material is used. In producing suspension fertilizers, in which small suspended particles of fertilizer solids are present, use of more highly soluble fertilizer materials allows for more plant food to be in solution and less to be present in solid form at a given temperature than when a less soluble material is used. Since the viscosity of suspensions generally increases with increase in the proportion of solids present, and high viscosity is usually the factor limiting the grade of suspensions, higher-grade suspensions can generally be made with more soluble materials because more of the plant food is in solution and less is present in solid form. High viscosity characteristics tend to destroy the fluidity of such suspensions and render the transfer properties thereof, either by gravity or pumping distribution to the soil, rather impractical or indeed, impossible. It will be appreciated by those skilled in the art that suspension fertilizers with such low analysis have a very distinct economic disadvantage as compared with higher analysis products because costs of handling, freight, storage, and application are higher per unit of plant nutrient, all of which are factors of increasingly greater importance as costs associated therewith continue to escalate at a rate faster than certain other considerations, as for example, the costs of production of said fertilizers. It is therefore considered an advantage by those skilled in the art to use fertilizer materials which are highly soluble. However, numerous highly soluble fertilizer materials presently in use, such as urea and ammonium nitrate have the grave disadvantage that, their solubilities are drastically affected by temperature. Thus, when the temperature decreases, the proportion of solid particles present increases rapidly, due to the rapid decrease in solubility, and therefore the suspension viscosity increases rapidly. Therefore, such high grade suspensions which are perfectly fluid at room temperature can completely lose their fluidity at lower temperatures due to high viscosity.
In addition, use of highly soluble fertilizer materials which also have highly temperature-dependent solubilities results in growth of large crystals during storage, especially in situations where ambient temperature fluctuations of rather large magnitude occur. When the temperature rises, a large quantity of the fertilizer solids present go into solution. When the temperature subsequently decreases, thermal lag of the body of liquid and attendant slow cooling of same results in precipitation of a large quantity of fertilizer solids in the form of growth on existing crystals, rather than in the form of nucleation of new crystals, and the result is formation of excessively large crystals. Crystal growth has long been a problem in suspension fertilizers, especially when clear liquid layers of saturated solution form (syneresis) in the suspensions, which is common in nitrogen and nitrogen-sulfur suspensions. When the temperature falls, very large crystals form because the solubility decreases greatly in temperature and no crystals are present in the clear layer portion on which the resulting precipitating solid phase can grow. The result is often growth of the crystal ends at the clear layer interface out into the clear layer, resulting in formation of very large crystals. In the case of urea, growth of crystals in clear layers can result in crystal sizes which approach the dimensions of the storage container. Large crystals are intolerable in suspension fertilizers because they settle to the bottom of storage and shipping tanks, and they clog pumps and fertilizer application equipment.
Another disadvantage in fertilizer materials which are highly soluble and also have highly temperature-dependent solubilities is that diluting these products with water or mixing them with other fertilizer materials often alters the crystallization temperature of the material in such a way that the suspension is rendered unfit for storage due to growth of large crystals when temperature fluctuations repeatedly raise and lower the temperature above and below the crystallization temperature.
2. Description of the Prior Art
At the present time, because of the state of the art developed in view of and in response to said principal consideration supra, there are available a number of methods and means which utilize in one way or another the art of producing nitrogen-sulfur fluid fertilizers using ammonium sulfate and/or sulfuric acid and ammonia, some of which are represented by the investigations, teachings, and disclosures set forth in the following patents: U.S. Pat. No. 4,116,664, Jones, Sept. 26, 1978; Canadian Pat. No. 811,080, Ramaradhya, Apr. 22, 1969; U.S. Def. Pub. No. T101,803, Jones et al., May 4, 1982; U.S. Pat. No. 4,388,101, Lowder, June 14, 1983; U.S. Pat. No. 4,239,522, Wilson et al. Dec. 16, 1980.
Since fluid fertilizers containing sulfur are now needed in many regions of the country for soils which are sulfur deficient, procedures for producing fluid fertilizers containing both nitrogen and sulfur have been developed. One procedure for production of a liquid fertilizer containing both nitrogen and sulfur (as in Jones '664, supra) involves reaction of urea with sulfuric acid to form a liquid nitrogen-sulfate fertilizer comprising urea sulfate and liquefied urea. Sulfuric acid is added gradually to urea, which urea is preferably in powdered or prilled from, and added in controlled amounts to hold the temperature of the resulting reaction within prescribed limits. The sulfuric acid and urea form a resulting reacting molten slurry which is blended slowly during the reaction period. Sulfuric acid is gradually added until the total desired amount thereof has been added, and blending is continued until the slurry becomes completely liquefied. Water is subsequently added to produce desired products which will remain in liquid form at normal ambient temperatures. From the practice of this procedure, a resulting product of grade 31-0-0-9.7S will begin to solidify at a temperature of about 60.degree. F. If this product is diluted with water to a grade of 29-0-0-9S, the then resulting product will begin to solidify at about 10.degree. F. The pH of these products ranges from 0.4 to 1.0. By the practice of still another prior art procedure, a nitrogen-sulfur suspension was produced (as in Ramaradhya 811,080, supra). This procedure involved pregelling clay in urea-ammonium nitrate solution (32% N) and incorporating finely divided elemental sulfur in the solution-clay mixture by mixing in a tank with a propeller-type mixer. The grade of the resulting suspension was approximately 24-0- 0-23S, and the stability of the product was adequate for short-term storage.
Still another method for producing a nitrogen-sulfur suspension taught by Jones et al. ('803, supra) involves the reaction of sulfuric acid with gaseous ammonia and the simultaneous addition thereto of a urea-water solution in a single-stage reactor to produce a resulting boiling urea-ammonium sulfate solution. The boiling solutions are then rapidly cooled in two stages to about 100.degree. F. to produce therein an abundance of small urea crystals. The finished product is of grade 29-0-0-5S and contains mostly urea as the solid phase. Because of urea's high solubility and highly temperature-dependent solubility, urea crystals, as is generally well known, are subject to rapid growth to large sizes during storage.
In still another procedure, Lowder ('101 supra) produced nitrogen-sulfur solutions by first mixing sulfuric acid in water, followed by dissolving urea into the resulting acid solution, and finally by adding thereto anhydrous ammonia. However, because the products were solutions, in which the highest grades were limited by solubility, they were low in grade (19 to 25% nitrogen and 3 to 6% sulfur) and had rather high crystallization temperatures (32.degree. to 40.degree. F.) below which the products cannot be stored because the large crystals which form settle to the bottom of storage tanks or plug up solution application equipment.
In yet another procedure taught in the prior art, Wilson et al. ('522, supra) produced nitrogen-sulfur solutions containing urea, ammonium nitrate, and ammonium sulfate. Because these products were solutions, the grades were low relative to suspensions, and, because of ammonium sulfate's low solubility in UAN-32 (a urea-ammonium nitrate solution containing 32% nitrogen), the sulfur contents of these products were relatively low unless the nitrogen content thereof was drastically reduced.
There is no suggestion in the teachings of any of the above mentioned prior art references of the viable process and/or technique as well as the compositions resulting from the practice of the instant invention for the production of nitrogen-sulfur suspensions which (1) are produced with ammonium sulfate and/or a combination of sulfuric acid and ammonia; (2) contain ammonium sulfate solids in appreciable quantities and as the sole source of sulfur therein; (3) have their unexpectedly unique and very desirable physical properties and storage and handling characteristics; and (4) have their unexpectedly high grades and sulfur concentrations.